[OpenTRV-dev] H-bridge transistor selection

[Mike Stirling]

Yes. Drive each high-side transistor from the collector of the opposite low-side one. This also solves the problem of high-side drive when V+ is higher than logic level - not an issue in our case.

This topology leads to the following truth table (and no need for tri-state):

00 - Idle (all off)
01 - Motor run forward
10 - Motor run reverse
11 - Magic smoke (all on)

Mike
 
----------------original message-----------------
From: "Damon Hart-Davis" EMAIL ADDRESS HIDDEN 
To: "Closed list for developer discussions" EMAIL ADDRESS HIDDEN 
Date: Thu, 16 May 2013 12:30:46 +0100
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> Hi,
> 
> I *should* be confident with this, but I am not.
> 
> Is it possible to run a bipolar H-bridge from 2 tri-state outputs properly 'class 
> C' ie avoiding ever having shoot-through by being able to let all four 
> transistors be off at once?
> 
> It's trivially possible with 4 tri-state outputs, or even 4 non-tri-state 
> outputs.
> 
> Rgds
> 
> Damon
> 
> 
> On 16 May 2013, at 11:38, Stuart Poulton wrote:
> 
>> On 16/05/13 11:32, Mike Stirling wrote:
>>> Interesting. The poor performing transistors do so because he is running 
>>> them far too hard, although he does acknowledge this. He is also running out 
>>> of gain at the lower voltages, and would get an improvement there by reducing 
>>> the value of the 1k base resistor. This is evidenced by the reduction in 
>>> voltage drop with increasing supply voltage. The important figures in the 
>>> datasheet are Ic from the absolute max ratings, which needs to be well above 
>>> the expected stall current of the motor, Vce-sat, which should be small, and 
>>> the worst case hFE (large signal current gain), which should be high enough 
>>> to allow for an acceptably low base current during motor stall conditions. 
>>> Mike 
>> 
>> Mike,
>> 
>> Coming up with a nice H-Bridge for battery operation would be great, esp if it 
>> could be driven with a low pin count from a uP.
>> 
>> I did measure the stall current of my dissected TRV head,
>> 
>> 2 - Motor run current (no load) 13-15mA
>> 3 - Motor Stall current - 95-100mA
>> 
>> Cheers
>> 
>> Stuart
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